High frequency telecommunications semiconductor devices for low impedance RF transmission circuits require very low inductance interconnections between the chip and the circuit board. Frequently, integrated circuits designed for these applications are also relatively high power devices. Semiconductor devices that dissipate high power, or are used in high frequency telecommunications, are usually packaged with a heat sink to dissipate heat produced by the device and to provide a RF ground plane for the device. The heat sink is positioned close to or against the semiconductor device and is encapsulated within the device package with one surface of the heat sink exposed through the package encapsulant. The addition of a heat sink along with a lead frame requires additional components, additional assembly steps, and additional equipment, thereby increasing the cost of the device.
Previously, packages for RF transmission circuits included hermetic packages for military application, and more recently packages having the die mount pad of the leadframe exposed through the plastic encapsulant, or having a custom leadframe with wide ground connections. The latter packages make attempts to compensate for the shortcomings of known high frequency and/or high power packages, and have been disclosed in U.S. Pat. No. 5,594,234 issued Jan. 14, 1997 and U.S. Pat. No. 5,663,597 issued on Sep. 2, 1997.
In high frequency applications the semiconductor package has the greatest influence on total performance of the circuit, and one of the main causes of performance degradation is inductance of the interconnections between chip and printed wiring board. Therefore, as the operating frequency of these circuits increases there is a need for even lower inductance packages, some of which may require less than 50 ohms matched impedance.